This invention relates to a machine for sealing a lid on a container, as for sealing food or the like in the container.
Food containers used by fast food establishments, grocery stores, delicatessens and the like, when filled on site, commonly employ a tray-type container integrally connected to a cover or lid. These containers are handy but do not seal the food in or seal air out. Consequently spillage readily occurs and retention of freshness is not possible. Another type of common container is that which has a separate lid which is snapped into place between the specially formed lid and container. Some containers of this type are leak resistant, but do not totally seal the contents. In large food processing establishments, containers can be completely sealed utilizing sealing machines which are presently known, but these typically are complex apparatuses, not suitable for on-site use in fast food restaurants, grocery stores, and the like. Persons employed at fast food establishments and the like are frequently young, relatively unskilled persons who work at a rapid pace. Turnover rate of employees is generally high, resulting in a high level of inexperience. Therefore, any mechanical devices to be used to close and seal containers at these establishments should be simple, easy and safe to use. There is needed an apparatus which meets these criteria as well as providing a leakproof or leak resistant container which also preserves freshness of the food item.
One type of known apparatus usable in grocery stores, to seal a polymeric film lid onto the top rim of a container for containing and transporting food, uses a heated platen. If the tray is plastic, it can be made leakproof and airtight. If it is paperboard, it can be made leak resistant. The apparatus involves a fixed lower support serving as a tray carrier and having a well or cavity to receive and retain a container therein, and the upper heated platen pivotally mounted to shift to a closed position on the container and lid between the platen and the lower support. The heated platen is manually forced down and held down by the weight of the human operator onto the container and lid during a time period while heat is applied to seal the lid to the container.
However, in order to provide sufficient force on the container and lid to fully compress the periphery of the two together, the heated upper platen must be manually forced down by the operator with a significant force which is usually about 20-40 pounds. By using leverage-type mechanical advantage, the force applied to the container and lid can be about 75 pounds. This exertion is required for each tray and lid, and for a set time period, in order to force the platen and tray carrier fully together. Establishments which would use these units frequently employ teenage persons or ladies, so that applying this significant amount of force steadily on the platen is difficult, requiring considerable exertion, and is particularly tiring. Moreover, it has been determined that even the application of this much force is sometimes not sufficient to assure a complete seal of the lid periphery to the container periphery. To be certain of sealing, the force should actually be several times this amount. One of the variables that can prevent total sealing is the fact that the flange of the tray might not be of uniform thickness around its periphery, resulting in a poor seal at the thinner areas.